1. Field of the Invention
The invention relates to a device for the contactless charging of an electrical energy storage of a motor vehicle, comprising at least one primary coil that can be connected to an electrical power supply system, and a bottom housing, within which the primary coil is arranged. The device is formed so that the primary coil can be flowed through by an alternating current during operation and can generate an alternating magnetic field that can induce an alternating electrical voltage in a secondary coil on the vehicle that is separated from the primary coil by an air gap. As a result, a current flow that is variable over time and can be converted by a rectifier on the vehicle into a direct current for charging the electrical energy storage connected to the rectifier.
2. Description of the Related Art
Alternative drives are playing an increasingly greater role in motor vehicle technology.
The prior art discloses motor vehicles in which the drive comprises an electrical machine or a combination of an electrical machine and an internal combustion engine (known as hybrid electric vehicles). Such motor vehicles have an electrical energy storage for storing electrical energy that is used for feeding the electrical machine.
The electrical energy storage typically has an electrical voltage level in the range between 200 V and 400 V, and has a multiplicity of chargeable battery cells or chargeable blocks of battery cells that are connected to one another.
Various approaches to charging the electrical energy storage are known from the prior art. Charging often is performed with the aid of a charging cable that can be connected to a charging interface of the motor vehicle and to a charging interface of a public power supply system (known as plug-in technology). The charging interfaces of the public power supply system often are standardized sockets, into which a conventional charging plug of the charging cable can be inserted. The charging operation on the public power supply system always requires intervention by the vehicle user, since the charging cable has to be inserted into the charging interfaces provided for it, as a result of which they are subject to wear. Charging of the electrical energy storage of the motor vehicle is not possible if the vehicle user inadvertently leaves the charging cable behind.
Charging stations in areas that are accessible to the public often are damaged by vandalism.
To remedy the aforementioned problems, the prior art has considered using induction for contactlessly charging the energy storage of a motor vehicle. This approach requires two coils. A first or primary coil is accommodated in a bottom housing and is connected to a public power supply system. A second or secondary coil is positioned in the region of an underfloor of the motor vehicle. The primary and the secondary coils must be positioned as exactly as possible over one another for charging the electrical energy storage of the motor vehicle, and consequently must be aligned with one another in the x, y and z directions. The primary coil on the bottom side is flowed through by an alternating electrical current for charging the electrical energy storage means. The primary coil generates an alternating magnetic field that induces an alternating voltage in the secondary coil on the vehicle side, with the consequence of a current flow that is variable over time. A rectifier is provided on the vehicle side to bring about a rectification of the alternating current, so that the electrical energy storage means can be charged.
The distance between the primary and secondary coils in the z direction (vertical direction) can be varied by using a scissor-like lifting device arranged in the bottom housing. The size of an air gap between the primary and secondary coils can be varied in a defined way and set appropriately by raising the primary coil.
Modern motor vehicles often are equipped with a height-adjustable chassis so that at least two different height levels of the motor vehicle can be set. The height-adjustable chassis may for example comprise a height-adjustable air suspension device. WO 2014/114762 A2, WO 2012/079668 A2 and in US 2012/0025761 A1 disclose that the height-adjustable chassis can be lowered before the beginning of the charging process for setting the distance between the bottom-side primary coil and the vehicle-side secondary coil, and consequently setting the size of the air gap. When the device described above is used for the contactless charging of the electrical energy storage of a motor vehicle that has a height-adjustable chassis, the setting of the air gap can be performed according to choice by lowering the height-adjustable chassis or by raising the primary coil with the aid of the lifting device. A combination of the two height adjustments (i.e. lowering the height-adjustable chassis and raising the primary coil by the lifting device) is conceivable in principle. This may be required for example in the case of a motor vehicle with a relatively great ground clearance, such as an off-road vehicle, if the lowering of the motor vehicle by means of the height-adjustable chassis is not sufficient to set the air gap between the primary coil and the secondary coil to the required value.
In principle, the lifting device within the bottom housing may be omitted if the motor vehicle can be lowered by the height-adjustable chassis to the extent that the air gap between the primary and secondary coils can be set to the corresponding value.
The air suspension device on a motor vehicle that has been in service for a relatively long time may sag. Sagging of the air suspension device may cause the motor vehicle to set down on the primary coil and may cause damage to the coils.
An object of the invention is to develop a device for the contactless charging an electrical energy storage of a motor vehicle in a way that prevents damage that may be caused by the motor vehicle setting down on the primary coil.